Control apparatus



Aug. 1946- c. A.BLAKESLEE 7 CONTROL APPARATUS Filed Jan. 11, 1944 IN VEN TOR.

Patented Aug. I3, 1946 CONTROL APPARA'IUS Clinton A. Blakeslee, Waterbury, Conn., assignor to The Bristol Company, Waterbury, Conn., a corporation of Connecticut Application January 11, 1944, Serial N0. 517,808

19 Claims. 1

This invention relates to automatic control mechanisms, and more especially I;o a device wherein the control point of a regulating mechanism operated by a measuring Instrument of the self-balancing potentiometer dass may readily be adjusted through a wide range and use of a high degree of precision. In U. S. Letters Patent N0. 2326238, granted I;o A. R. Mabey, August 10, 1943, obere is disclosed a method whereby a pneumatic control device may effectively be rendered subject 120 a. recording instrument of the potentiometer dass having a chart With rectangular coordinates. The present invention invo1ves the application 015 a differentia] principle to the actuation of a control device from a. selibalancing Instrument having circular coordinates; and while it is applicable 120 other forms f control, is especially adapted for use in a coutrol system wherein modulation is efiected by varying I;he condition of an electri cal circuit.

It is an object of this invention to provide a difierential control mechanism readily adaptable I:o coordination with a self-balancing measuring instrument.

II: is a further object 130 provide such a, mechanism in a form which sha11 be inherently free of backlash between the control and actuated elements.

It is a further object to provide such a mechanism in a form especially adaptable to modulated regulation of the electrical type.

II; is a further object so provide such a. mechanism in a form which sha1l be readily adjustable to any desired control point, and Which shall show a. consistent performance at all settings.

In carrying out the purposes of the invention it is proposed to provide a measuring and controlling Instrument having two identical cam members movable by the measuring element; and the setting mechanism respectively, said cam members being mutually disposed in a manner 110 act joint1y upon a diflerential mechanism which is simultaneously in engagement with their respective peripheral surfaces. The degree of actsivity of the controlling mechanism is made responsive to the displacement of said difierential mechanism as produced by the relative positioning of said cam members. The element of the contro1 mechanism which is directly in engagement with the differential mechanism preferably takes the form of a slide-wire rheostat forming a part of a bridge circuit; and I:o this circuit may be applied various compensating and anticipatory devices which, while not forming parts of the presentinvention, are sometimes desirable in coujunction with control systems to which Ishis invention is especially applicable.

The single figure of the drawing represents an embodiment of the invention whereby an electrically-operated valve may be operatively associated with a temperature-measuring instrument of the potentiometer dass.

Referring now to the drawing: v

The numeral III designates a furnace, oven, 01 other enclosed spa.ce adapted to be heated by the combustion 0f fiuid fue1 admitted thereto through a burner II, and in which it is desired to maintain a predetermined constan temperature as measured by a thermocouple I2 located Within the furnace, the regulation of said. temperature being effected by control of the position of a valve I3 connected in a conduit I4 through which said fuel is supplied 130 the burner from a source I5. The va1ve I3 is actuated by a reversible electric motor I'I having three ter minals I8, I9, and 20. Ehe internal connections of the motor are made such that When voltage from. a suitable source is applied to the terminals I8 and I9 the motor will rotate in a sense 120 close the valve I3, and when said voltage is applied the terminals 20 and I9 the motor will operate in a sense to open said va1ve. A slide-wire rheostat 2I, having terminals 22 and 23 is operatively engaged by a sliding contact 24 attached to the mechanism 0f the valve I3 and moved therewith by I:he motor I'I in a sense that as said valve is moved toward a closed position the contact approaches the terminal 22 and as said valve is opened the contact approaches the terminal 23.

Mounted upon a base-plate 25 is a circular slide wire structure 2G, electrically engaged by a movable contact or slider 2'I, carried. by an arm 28, which in turn is attached to a rotatable shaft 29 passing centrally through the slidewire structure 26 and journaled in the base-plate 25, whereby, with rotation of the shaft 29 the contact 21 may traverse the length of the s1ide wire. For purposes of clarity in the drawing, the active length of the slide-wire is shown as occupying a comparatively small portion of I:he periphery of the structure; but it Will be understood that its active length may be increased as desired in practice. The slide wire 26 forms a part of a conventional potentiometer circuit, including a battery 30 adapted to app1y a constant potential to ehe slide-wire terminals, and a contact-making galvanometer 3I. The thermocouple I2 is connected between a terminal of slide wire 26 and the galvanometer 3I; and the electrical arrangement of the network is made such that by movmg the siiaer 271 with respect to the slidewire there may be obtained a condition of balance as cletected. 'oy the galvanometer 3 l, Wherein the ps1t1on 0I' the slider With respect to the slide-wire becomes a measure of tne poteninal existing between the terminals of the thermocouple E2, ancl therei'ore oi the temperature to Whi0h n; is exposed;

Rotation of the shaft 29 is effected through suitable gearing 35 by means of a reversible electric motor receivmg power from a source 37 and controlled by relay means 38 direciy subject to the defiection 0f the galvanometer 3l. The mechanism and means for balancing the potentiometer network through rotation o1? the shaft 29 in response to the detection of an unbalanced conolition by the galvanometer 52 may, for example, be of the form fully set iorth and. described. in U. S. Letters Patent N0. 232-0066 issued to F. B. Bristol, May 25 1943; and since this and. other forms 0I" electrical self-balancing mechanisms are well known in the art, no further explanation cf that element of the device need "leere be given.

Fixed 130 the shaft 29 is a pinion 35 meshing With a gear sector l integral With a shaft 4l journalecl in the base platze 25. Attached 'to the shaft il, and cleflectable With the rotation thereoi through a limitecl angle, is an extencled arm 42 carrying a pen or stylus 33 adapted t0 transverse the iace of a gracluated record chart M, and to inscribe thereon a trace of its movements. The chart 54 is driven at a constant velocity by means of a conventional timing mechanism not sl1own in the drawing, whereby the trace made by the pen or stylus 63 becomes a graphic record of positions assumed by said pen or stylus, and. therefore of the temperatures existing within the furnace or oven l!l over a periool oftime.

Journaled in a bracket member 55 integral With the base-plate 25 (which bracket member mal also form auxiliary bearings for the shafts 29 and li) is a shaft 46 coaxial With the shaft 29 and adapted for angular adjustment about its axis by means of a knob M. ixed to the shaft 655 is a pinion 48 meshing With a gear sector 48 journaled upon a bracket 59 integral With the base-plate 25, and rotatable through a limitecl angle about an axis parallel to but displaced from the axis of the shaft 1l. Attached to the gear sector i% is an extended arm l terminating in an index er pointer adapted to traverse the graduated surface of the chart 44, and t0 follow a tirne graduation upon said surface, laut, by Virtue et. the displacernent of the axis of the shaft 45 from that of the shaft M, not in any position intersecting the path cf the pen or stylus 43.

Fixecl to the shaftg 29 and 66 respectively are cams 55 and 5-5, angularly rotatable With said shafts in parallel planes and having their peripheries conformed to identical spiral contours whereby the length of any selected radius Will be proportional to its angular displacernent from a selected reference radius.

Journaled upon the bracket 50 and rotatable through a limited angle about an axis 51 parallel to, laut displaced from, the cornmon aXis of the shafts 29 and 45, is a rocker-arm structure 58 having a projecting portion 58 extendecl beyond said common axis and carrying a pivotally mountecl shaft or spindle 59 rotatable through a limitecl angle about an axis intersecting the axis 57 anal said last-named axis. Fixed to, and. extending traversely from, the shaft 59 is a cross-arm 60, carrying on its extremities cam-followers or rollers l and. 62 engaging the peripheries of the Cams 55 and 56 respectively.

Extending from the rocker arm structure 58 in a sense substantially perpendicular to the projection 58 is a bracket 65 carrying on its extremity a slide-Wim resistance EG. Fixen. to the shaft or spinolle 59 and. defieetable therevvith, is an extencled arm 67 bearing an insulated contact 58 adaptecl to traverse said slide-wire and to assume with respect to the extended length thereof a position dependent upon the angular defiection of said shaft about its axis of rotation. A tensidn spring S9, extended. between the bracket 65 and a fixed abutment on the base-plate 25 maintains the followers 81 and 52 in definite engagement With cams 56 and 55 respectively, and effectively eliminates backlash from the mechanism.

Connected to the motor l'l of the valve I3 is a relay member 70 having a sensitive winding and ci1*cuit-controlling elements (not shown in the drawing) whereby said circuit-controlling elements Will be actuated in a sense dependent upon the direction of current flowing in said Winding. The relay member Hi is interconnected with the slide-Wire resistors 2I and 65 and a source of electrical energy H to form a briclge circuit; and the circuit controlling elements of the relay are connected to said source of energy and to the motor 20 in such a manner that unbalance cf the briclge circuit due to motion of the sliding con tact 58 along the slide-wire 66, Will cause the relay member 10 to respond and actuate the motoi 253 in a sense to cause the contact arm 24 by its movement With respect to the slide wire 2! reestablish balance in the bridge network. 'Ihis is a conventional and well-known form of nontrol, and is found in many clevices for distant regulation of motors. An early exarnple of such a control is disclosed in U. S. Letters Patent N0. 599,903 granted to M. Pfatischer, May 12 1896, where the principle is shown in its application to the steering of ships. For tliis element of the control system forming a part 0f the present invention no novelty is claimed; and lt neeol not here be further described.

The operation of the apparatus embodying the principle of the invention may be described as follows:

Assuming iirst that there exists a conclition of equilibrium, with the valve I3 set at such a position ag t0 admit to the burner l I sufficient fue1 maintain the space within chamber lfl at a preoletermineol constant temperature as detected by the thermocouple 12 and measured by the position of the sliding contact 21 With respect to the slidewire 26, the shaft 29 and the cam 55 will be maintained in position representative of said temperature, and the arm 42, actuated through the shaft ll from the co-acting gear members 39 and 4'5l, Will position the pen er stylu 43 upon the graduated surface of the chart 44 to provide a measure of said temperature value. By previous acljustrnent the angular position of the carn 55 about the common axis 0f the shafts 29 and 56 Will be the same as that of the cam 55, so that the cam followers 6! and 62 resting upon the camg 55 and 56 respectively Will be at a common radial distance from said axis, and the shaft 59 subject 170 the joint influenee of said cam followers will cause the arm 61 to occupy an intermecliate position whereby the contact 63 carried thereby will rest upon the slide wire 56 in a'locatioh to maintain a balanced condition in the bridge circuit which includes the slide wire 2l; and the valve motor I? will remain al; rest.

I*s may now be assumed that there has develeped a condition tending to lower the temperature Wifihin chamber I0. The E. M. F. developed by the thermocouple I2 will be correspondingly lowered with a resultant disturbance cf the potentiometer balance, whereby current Will fiow throu-gh the sliding contact 21 and l31le galvanometer 3 i. The response of the galvanometer will 'ee such as to actuate the relay 38, according t-o principleg hereinbefoie sei; forth, in a sense to cause the motor 36, acting thrugh the gear train 35t0 roiate the shaft 28 in counter-clockwise sense as seen in the drawing, and to shift the sliding contact 21 to a position 0f lower potential along the slide-wire 25, whereby electrical balance cf the potentiometer network will be restored. "Ehe shaft 41 will have been correspondingly rotatecl and the pointer arm 43 moved 130 a position where the pen er stylus 43 Will provide 011 the chart 44 a measure cf the newly attainerl temperaturevalue.

'Ine cam 55 will have been corresponciingly rotatecl in a counter-cldckwise sense, so as to cauee follewer l to engage a portion 01 ics periphhaving an inereased radius. The movement f the iolievver l, aeting througlrthe cress arm E9, Will cimse seid arm tasWing abcut the point of eneagement of the follower 62 wibh the periphery of Elle cam 56 as a fulcrum, whereby be shaft 59 and the rccker-arm structure 58, will be given b0dily rotaizion about the axis 52', carrying il1e braclzes 85 anal the slide wire 66 through a CO1- respenriing limited angle about seid axis. A5 seid roary metion is derived from a change in position cf ene end only of the cross arm 653, the consequerit'angular rotation of the s'naft 59 With respectco l3lle rocker-arm strueture 53 Will cause the 5? to be similarly rotatecl, Whereby the contact Wlzl assume a new position With respect to the slide wire 68, the change in position being iowarcl the right as seen in the drawing.

'I'he chan' e in position 01 che contact 58 With respeet t0 the slicle Wire 36 Will disturb the balance of the bridge circuit comprising said slide Wim 68 and Ehe slide wire 2I, whereby the relay Will be energize-cl in a sense t0 actuate the va1ve motor i? and open the valve I3, causing an increaeed supply o=f Iuel to be admitecl from the source l% through the conduit 4 to the burner i l, with a corresponding tendency torestore the temperature within the chamber 53 to its former preCle-ermined val'ize. At the same time, the nontac+ arm 231 will have been shifted along the slide wre 2i in a senee to resbore the balance o-f the bridge eircuit and render ihe relay 'i'0 inactive, so th-at alle valve motor I'. Will be brought to resa with th-e valve i3 in a new position correspsnding to he increased demand for fuel.

In a eimilar marmer, shoulcl the temperature wi'nn ehe chamber rise above ehe predetervalue, ehe resuliant increased potential developed by the thermecouple I2, acting upon 'uhe galvanometer 31 through slidin-g contact 21 of the poteniiomeier circuit, Will cause the relay 31 t-o reeponcl ancl to actuate the motor 35 in a sense 130 restore the potentiometer balance by rotating the shaft 29 in a cl-ockwise sense as seen in the dravvine ancl shifting the sliding contact 27 towarcl ihe right on the slide wire 25, which change Will b-a indicated by pen er stylus 43 assuming a new position 0:1 the chart 44. As the same time, the cam being rotatecl in a clockwise sense, Will present a decreased radius 170"13h8 folloWer EI whereby the cross arm 66 will be rotatedabouf; the point of engagement of the follower 62 with the cam 48 as a fulcrum, causing the rocker-arm structure 58 to be retated in a clockwise sense about the axis 51, and the slmft 59 at the same time so be rotated With respect tosaid rockerarm strucure in a sense t0 move the arm 6'! ancl the conbaci; 88 carried thereby, toward the lef5-hand end of the slide wire 6%. This action Will cause izhe bridge network comprising saicl slide Wire 65 and slidewire 2l tobecome unhalance-d, whereupon the relay 76 will act to operate the motor I! in a direction 130 close the valve I3, andr-incidentally to restore the bn'dge balance by moverneni; of the contact arm 24 with re'speci 130 the slide Wire 2I.

It will thus be seen there has been provicled. a mechanism which will continually tend regulate th'e conditions Within the chamber l000 a constant temperature. It Will further be apparent that the temperature toward which regulation is eifected may be established at-any clesirecl predetermined value by manual adjustment of the angular position of the cam 56 by means of the knob 41. 'Ihe pointer 5l, angularly movable with the gear sector 49, Will be subject to displacement with any change in the setting of the cam 56, so that itmay be ca'used toprovide on the graduated surface of the Chart 44 an indication of'the control point established. by the setting cf the cam 56.

The terms anti expressions whichl have employed are usecl as terms of description and not 015 limitation, andl have no intention, in the use o.f such terms and expressions, of excluding any equivalents of the features shown and described er portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

I claim:

1. In a device for controlling the magnitude of a variable, a measuring instrument sensitive to changes in said variable, a cam, means comtrolled by said instrument for positioning saicl cam in aceordance with said magnitude, a second cam, means for positioning said second cam in accorclance with a desired magnitude, dilferential means cooperating With said cams and operable thereby into positions corresponding w differences between the settings of said cams, and means controlled by saicl differenoial means for afiecting ehe magnitude o:f said variable.

2. In a device for controlling the magnitude of a variable, a measuring instrument sensitive to changes in said variable, a cam, means controlled by said instrument for positioning said cam in accordance With said magnitude, a second cam having a working surface substantially identical With that of the first mentioned cam, means for positioning seid second cam in accordance With a desired magnitude, differential means cooperating with said cams and operable thereby into positions corresponding to differences between the settings of saideams, and means controlled by saic1 differential means ior affecting the magnitude 'of said variable. 1

3. In a device for controlling the magnitude of a variable, a measuring instrumeni; sensitive t0 changes in said variable, a cam, means comtrollecl by saicl instrument for positiomng said cam in accordance with saiol magnitude, a second cam having a working surface substantially identical with that of the first mentioned cam and movable in a plane substantially parallel to thatcf saidfirst: mentioned cam, means for positioning said second cam in accordance with a desired magnitude, difierential means cooperating with said cams and operable thereby into positions corresponding 110 difierenceg between the settings of said cams, and. means controlled by said difierentia1 means for afiecting the magnitude cf. said variable.

4. In a device for controlling the magnitude of a variable, a measuring instrument sensitive to changes in said. variable, a cam, means controlled by said instrument for positioning said cam in accorolance with said magnitude, a second cam, means for positioning said second cam in accorclance With a desired magnitude, differential means eooperating simultaneously with saicl carns and rockable thereby about an axis into positions corresponding 130 differences between the settings of said cams, and means controlled by said differential means for afiecting the magnitude of said variable.

5. In a device for controlling the magnitude cf a variable, a measuring instrument sensitive to changes in saicl variable, a cam, means controlled by saicl instrument for positioning saicl cam in accordance With saicl magnitude, a second cam, means for positioning saicl second cam in accordance with a desired magnitude, difierentia] means comprising a rockable shaft having extensions engaging said cams and rockable thereby into positions corresponc'ling to dififerences between the settings of said carns, and means coutrolled by saicl differential means for affecting the magnitude cf said variable.

6. In a device for controlling the magnitude f a variable, a measuring instrument sensitive 110 changes in said variable, a cam, means coutrollecl by said instrument for positioning said cam in accordanee with said magnitude, a second cam, means for positioning said second cam in accordance Wibh a desired magnitude, differential means cooperating simultaneously with saicl cams and movable thereby into positions corresponding 110 difi"erences betvveen the settings of said cams, a frame carrying said differential means and movable by said cams, control means movable with said differential means and said frame respectively, and means controlled by said control means for afiecting the magnitude 01 saicl variable.

7. In a device for contr0lling the magnitude of a variable, a measuring instrument sensitive to changes in said variable, a cam, means comtrolled by said instrument f0r positioning said cam in accordance With said magnitude, a second cam, means f0r positioning said sec0nd cam in accorclance With a desired magnitucle, differential means comprising a rockable shaft haVing extensions engaging said cams and roekable thereby into positions corresponding to differenees between ehe settings of said carns, a frame carrying saicl differential means and rockable by said cams about an axis difierent from thal; of said rockable shaft, control means movable with said difierential means and said frame respectively, and. means controllecl by said eontrol means for afieeting the magnitucle of said variable.

8. In a device for controlling the magnitucle cf a variable, a measuring instrument sensitive ca changes in said variable, a cam, means controllecl by said instrument for positioning said cam in accordance with said magnitude, a second cam, means for positioning said second cam in accorda'nce with a desired magnitude, differential means cooperating with said cams and oper- 8 able thereby into positions corresponding todifferences between tl1e settings of said cams, reversible electric -motor means for affecting the magnitude Qi said variable, and electrie circuit means controlled by saicl differential means for controlling the operation of said motor.

9. In a device for controlling the magnitude of a variable, a measuring instrument sensitive to changes in said variable, a first cam member movable under control cf said instrument, a second cam member having a working surface substantially identical with that of said first cam member and adjustable in a plane parallel to that o-f saicl first cam member, a rocker element rotatable through a limited angle about an axis perpei1dicular to the planes of said cam members, said rocker element having pivoted thereon an extended differential member with its extremities simultaneously engaging the respectiVe cam members, first control means carried by said recker element, second control means movable with respect 130 said. first control means in response to variations in the angular position of said differential member about its axis, and means controlled by said first and sec0nd sontrol means 130 affect the magnitu'de of said variable.

I0. In apparatus for controlling the magnituoleof a variable, a measuring instrument having a movable element adapted to assume a position representative 0f the magnitude of a couclition 130 be controlled, a first cam member movable With said element, a second cam member movable in a plane parallel 130 that of said first cam member, a rocker-arm rotatable through a limited angle about an axis perpendlcular the planes cf saiol cam members, said rocker arm having pivoted about an axis thereon an extendecl differential member With its extremities engaging saiol cam members and means carried by said rocker arm and adapted to affect the magnitude 0f said variable according to the defiection of said differential member about its pivotal axis.

ll. In a device fr controlling the magnitude of a variable, a measuring instrument sensitive 110 changes in said variable, a first cam member movable under control 0f said instrument, a second cam member having a working surface substantially i'dentical with that of said. first cam member and adjustable in a plane parallel to that of said first cam member, a rocker element rctatable through a limited angle about an axis perpendicular to the planes of said cam members, said rocker element having pivoted thereon an extende ol differential member With its extremities simultaneously engaging the respective cam members, first control means carried by said rocker element, second control means movable with respect to said first control means in response to variations in the angular position o-f said differential member about its axis, and means controlled. by said first and second C011- t1'01 means to afllect the magnitude of saia variable, separate indicating means associated respectively with said. cam members, and movable 110 provide indications of the measured magnitude 0f said variable and the setting of said second cam member respectively.

12. In an instrument for measuring and coutrolling the magnitucle of a variable condition, means sensitive 130 changes in said magnitude, a graduated. sv.rface a firsl; deflecting member juxtaposed said surface and adapted to provide thereon a measure of said magnitude a first rotatable element controlled by said sensitive means for posltioning said member With respect to the graduations 011 said surface, a second deflecting member juxtaposed to said surface and adapted to provide in conjunctlon with tl1e graduations thereon measures corresponding to desired magnitudes of said conclition, a second rotatable element operable cencurrently with the positioning f said second eleflecting mernber, difierential mechanism comprising two similar cam members and a follower jointly positioned by the sarne, one of the said cam members being connected 170 the first rotatable element for movement thereby, and the other of the said cam members be ing conn@cted to the seconcl rctatable element for movement thereby. ancl means actuatecl by said follower for controlling said variable conclition.

13. In apparatus for controlling the magnitude of a variable, a measuring instrument having a movable element adapted to assume a position representative of the magnitucle of a condition to be controllecl, a first cam member movable With said element in a plane, a second cam memher movable in a plane parallel to that 01 said first cam member, a rocker-arm rotatable through a limited angle about an axis perpendicular to t-he planes 0f said carn members. a variable resistance unit carrie i loy said rocker arm, an electrical netwerk including said re sistance unlt and means fer controlling said magnitude whereby changes in said resistance unit will aifect the performance of said controlling means, and means movably carried upen said rocker arm and positionecl relatively thereto under the joint influence ofsaid cam elements to vary said resistance and thereby to command the Operation 01 said controlling means.

14. In a clevice for controlling the magnitude of a variable, an electrlc motor adanted to control said magnitude, a control circuit for said motor including a resistance element variable by said motor and a directlonal relay adapted to command the operation of said unter, a measuring instrument havlng a movable element adapted to assume a position representatlve of said magnitude, a first cam member movable With said element a second cam member movable in a plane parallel to tliat of said first cam element, a rocker-arrn rotatable through a limited angle abeut an axls perpendlcular to the planes of said cam mem'oers, said. rocker-arm havlng pivotally mounted thereon a differential member adapted 130 be angularly posltioned by t-lie joint infiuence of said first and second. cam members, ancl resistance means variable in accorclance With the angular position 0.1" said dliferential member and connected in said contr0l clrcuit t0 form With said first resistance element a briclge network with said relay directionally respensive to unbalance conditions t0 command the operatlon of said motor in a sense to restore the balance of said network.

15. In a device for controlling the magnitucle 0f a variable, an electric motor adapted to cantrol said magnitucle, a control circuit f0r said motor including a resistance variable by said mo tor and a directional relay adapted to command the operation 0f said motor, a measuring instrument having a movable element adaptecl to assume a position representative of said magnitude, means settable into a position representative cf a desired magnitude, dififerential means positioned under the jolnt control of said movable element and said settable means, and resistance means variable in accordance with the position 10 of said differential means and connected in said control circuit to form witn said first resistance a bridge network with said relay directionally responsive to unbalance conclitions to command the operation of said motor in a sense to restore the balance oi said network.

16. In a control systern for limiting the departure of tl1e magnitlicle cf a eonclltion from a predetermined value, tl1e cornbinatien of two cam members having slmilar eontours and. displaceable in parallel planes, one of said eam memleere being positionable at Will in accordance With said predeterrnined value, ancl the other having means ior positioning lt in accordance With said magnitude, an element retatable through llmited angles about twc axes, one of said axes lyln in a plane parallel to said planes, and the other bel:1 angularly disposed thereto, said rotatable element having parts c .gaging both said cams, whereby to be cleflecteci about the first of said axes in response to diilerences in the displacements of said cams, and to be defiected about the other of said axes to an extent proportional to the mean cf the effective helghts of said can1s, and means operatively connectecl ts said element for controlling said condltion.

17. In a control system for limiting tlie cl-eparture of the magnitude of a conclition from a predeterrnined. value, the combination cf two cam mernbers having similar contours anal angularly displaceable in different planes about a com1non axis intersecting said planes, one of said cams belng positionable about said axis at Will in accordance With said precletermined value, and the other having means for positioning lt in acc-ordance With said magnitude, an element rotatable through a limlted angle about tvvo axes, one of said axesl in-g in a plane parallel to said. planes, and the other bein angulaily disposed thereto, said rotatable element having parts engaging both said cams whereby to be defiectecl about the first of said two axes in res-ponse to difierences in the displacernents cf said carns, and to be deflected about the other cf said two axes to an extent proportional to the mean cf the effective radii of said carns, and means operatively connected to said element for controlling said condition.

18. In a control system for limiting the departure 0f tlie magnitude of a condition from a predetermined value, tl'1e combination of two cam members having simllar contours ancl displaceable in parallel planes, cne 01 said cam mernbers being positionable at Will in accordance With said predetermined value, and the other having means for positioning lt in accordance With said magnitucle, an element rotatalo-le through limited angles about two axes, one of said. axes lylng in a plane parallel to said planes, and the other being angularly disposecl thereto said rotatable element having parts engaging both said cams, whereby to be defiected about the first of said axes in response to difierences in the displacements cf said cams, and to be deflected. about the other of said. axes to an extent proportional to th.e means of the eifective heights 01 said cams, anal means operatively connected to said element for controlling said condition in response to defiectiou 0f said elemen't about said first axis.

19. In a control system for limiting the departure of the magnitude of a condition from a predetermined value, tne combination of two cam members having similar contours and angularly displaceable in different planes ab0ut a co-mmon axis intersecting said planes, one of said. cams being posltionable 'about said axis ab Will in ac- 11 oordance with said predetermined va1ue, and. the other having means for positioning it in accordance with said magnitude, an element rotatable through a limited angle about two axes, one of said axes lying in a plane parallel to said planes, and the other being angularly disposed. thereto, said rotatable element having parts engaging both said cams whereby to be defiected about the first of said two axes in response to difier- 12 ences in the displaoements 0f said cams, and. 120 be deflected about the other of said two axes to an extent proportional to the mean of the effective radii of said cams, and means operatively connected to said element fo1 controlling seiid condition in response to deflection of said element about said first axis.

CLINTON A. BLAKESLEE. 

